1. Field of the Invention
The present invention relates to an electric power tool in which a fastening torque is adjustable, such as a driver or a driver drill.
2. Description of the Related Art
In a conventional electric power tool of this kind, a clutch ring which is a part for adjusting the fastening torque is rotatably disposed on the body of the electric power tool, so that the fastening torque can be adjusted by rotating the clutch ring.
Such a clutch ring is requested to have a mechanical strength against an external force. Therefore, a conventional clutch ring is made of a hard synthetic resin such as polyamide (PA), polycarbonate (PC), or a material in which glass fibers are added to such a resin. A plurality of convex or concave portions are disposed in the circumferential direction on the outer peripheral face for the principal purpose of enhancing the antislipping function. Furthermore, characters or icons which indicate the adjustment state of the fastening torque of the electric power tool are printed on the outer peripheral face. In order to prevent the characters or icons from being defaced as result of use, recently, the character or icon portion is sometimes formed by two-color molding with using a hard synthetic resin of the same kind as that of the clutch ring.
A torque adjusting mechanism of an electric power tool having a clutch ring of this kind will be described with reference to FIG. 8. A pinion 10 which is fixed to a motor shaft 9 to be driven thereby meshes with planet gears A 12 which are supported by support shafts 11b of a carrier A 11, and which mesh with an internal gear A 14 fixed to a gear case A 13. In the carrier A 11, a sun gear A 11a is formed as the next stage. The sun gear A 11a meshes with planet gears B 17 which are supported by support shafts 15b of a carrier C 15, and which mesh with an internal gear B 16. The power of the motor shaft 9 is reducingly transmitted in a sequential manner to a sun gear C 15a which is formed in the carrier C 15 serving as the final stage. The sun gear C 15a meshes with planet gears C 20 which are supported by support shafts 19a of a carrier 19 that transmits a torque to an output shaft 18, and which mesh with an internal gear C 21. The internal gear C 21 is rotatably housed in a gear case B 23, and shaped so as to have a plurality of claws 21a which extend in the axial direction from an end face on the side of the output shaft 18. In the gear case B 23, a plurality of through holes 23b which elongate in the axial direction of the gear case B 23 and in places which can correspond to the claws 21a of the internal gear C 21. A ball 22 which is engageable with the claws 21a, and a cylindrical roller 24 which is positioned between the ball 22 and a clutch plate 25 are housed in each of the through holes 23b so as to be movable in the axial direction of the gear case B 23.
The clutch plate 25 is always urged toward the internal gear C 21 by the urging force of a clutch spring 26 which will be described later. The balls 22 are always urged toward the internal gear C 21 via the clutch plate 25 and the rollers 24 to attain a state where the balls 22 are engaged with the claws 21a by the urging force.
The gear case B 23 has a cylindrical shape having at least two portions of different outer diameters. In the outer-diameter portion, the carrier 19, the internal gear C 21, and the like are housed, and the through holes 23b which accommodate the balls 22 and the rollers 24 are formed. In the smaller-diameter portion, the output shaft 18 is rotatably supported, and a male thread 23a is formed on the outer periphery.
A clutch member 27 having a female thread 27a which is to be screwed with the male thread 23a is disposed on the outer periphery of the smaller-diameter portion of the gear case B 23. The clutch member 27 is turned in conjunction with turning of a clutch ring 1 which is turned by an external operation. The clutch member 27 is moved in the axial direction of the gear case B 23 with being turned by means of the screw coupling of the male thread 23a and the female thread 27a. The clutch member 27 receives one end of the clutch spring 26 which is interposed between the member and the clutch plate 25, and is moved in the axial direction of the gear case B 23 while changing the axial dimension of the clutch spring 26. The outer wall portion of the clutch member 27 is shaped so as to guide the inner diameter portion of the coil spring 26.
As described above, when the clutch ring 1 is turned, the clutch member 27 is moved in the axial direction of the gear case B 23 to change the axial dimension of the clutch spring 26. Namely, the tool is structured so that the axial urging force by which the clutch spring 26 urges the clutch plate 25 can be adjusted.
When the electric power tool is to be used, the urging force of the coil spring 26 is adjusted to appropriately select the sliding torque. When a load which is larger than the selected sliding torque is applied to the output shaft 18, the claws 21a of the internal gear C 21 axially move the balls 22 against the urging force of the coil spring 26 and the internal gear C 21 begins to rotate, and hence the power transmission to the output shaft 18 is interrupted. Namely, the torque transmitted to the output shaft 18 can be controlled by adjusting the compression amount of the coil spring 26 as described above. The transmission of a large torque to the output shaft 18 can be attained by shortening the axial dimension of the clutch spring 26, i.e., by compressingly turning the clutch ring 1, and that of a small torque to the output shaft 18 can be attained by turning the clutch ring 1 so as to lengthen the axial dimension of the clutch spring 26.
In the case of a driver drill, it is required to obtain a state where the sliding torque is not set, i.e., the state of a drill mode. This state can be attained by a configuration in which the balls 22 are caused not to be axially moved, by means such as that of fully compressing the clutch spring 26, or that of butting a part of the clutch member 27 against the clutch plate 25, whereby the engagement between the claws 21a and the balls 22 is maintained to block the rotation of the internal gear C 21.
A plate spring 28 on which protrusions to be engaged with recesses of the clutch ring 1 are disposed is interposed between the clutch ring 1 and the gear case B 23 in order to allow the clutch ring 1 to be turned by an external force but inhibit the clutch ring 1 from being freely turned. In this way, restraint is imposed on the rotation direction in order to prevent the clutch ring 1 from being accidentally turned by the urging of the coil spring 26.
As described above, restraint is imposed on the rotation direction of the clutch ring 1, and, in an operation of selecting the fastening torque, the clutch ring 1 must be turned against the restraint, and hence an operation force of a certain degree is required. In a selecting operation in the case where the fastening torque is to be increased, the coil spring 26 is compressed, and therefore it is requested to exert an operation force of a larger degree. In order to enable the clutch ring 1 to be surely gripped, conventionally, a convex or concave shape for antislipping is formed in the circumferential direction on the outer peripheral face of the ring. In the case where the antislipping function is to be sufficiently exerted, the antislipping shape strongly acts on the palm because the shape is configured by the same hard synthetic resin as that of the base member, thereby producing a problem in that it is impossible to comfortably grip the ring.
The invention has been conducted in view of the above-mentioned circumstances. It is an object of the invention to provide an electric power tool which has a necessary and sufficient antislipping function, and which provides a gentle touch to the palm, i.e., in which the torque adjustment can be conducted surely and comfortably.
In order to attain the object, according to the present invention, there is provided an electric power tool in which an outer member has a plurality of projections discontinuously arranged on an outer peripheral face of a base member of a clutch ring, the outer member being lower in hardness than the base member.
In the electric power tool, the projections of the outer member are coupled to one another on a front side in an axial direction of the clutch ring.
In the electric power tool, the respective projections of the outer member are inclined with respect to a turning axis of the clutch ring.
In the electric power tool, a groove is formed in a surface of each the projection of the outer member, in parallel with a turning axis of the clutch ring.
In the electric power tool, the respective projections of the outer member radially project beyond the base member.
In the electric power tool, a rounded shape is formed in a projecting edge of each the projection of the outer member.
In the electric power tool, an annular member which is larger than a maximum outer diameter of the outer member is formed on an outer periphery of the base member to be integrated with the base member, and end portions of the projections of the outer member are inserted into the annular member.